1. Field of the Invention
The present invention relates to a sheet for electrophoretic display devices, a process for its production, and its applications. More specifically, the present invention relates to a sheet for electrophoretic display devices and a process for its production, as well as, electrophoretic display devices obtained using the sheets for electrophoretic display devices, and electronic equipments obtained using the electrophoretic display devices.
2. Description of the Related Art
An electrophoretic display device displays character data, image data, and the like, by the behavior of electrophoretic particles, for example, when a voltage is applied to a dispersion in which the electrophoretic particles are dispersed in a solvent. For example, if the electrophoretic particles and the solvent are colored with different colors, the color of the electrophoretic particles is observed when the electrophoretic particles are moved to the surface of the solvent by voltage application, and the color of the dispersion is observed when the electrophoretic particles are moved to the bottom of the solvent. If electrodes are provided to which voltage application is made possible by address appointment, different colors for the respective addresses can be displayed, and accordingly, arbitrary character data and image data can be displayed. Moreover, it is possible to rewrite the display data, and at the same time, it is advantageous that the display data can be maintained as it is, even if there is no electric signal.
In recent years, in place of the conventional electrophoretic display devices (e.g., see Japanese Patent Publication No. Sho 50-15115) in which a dispersion of electrophoretic particles are enclosed in spaces between opposed electrode substrates, there have been developed microcapsule type electrophoretic display devices (e.g., see Japanese Patent No. 2551783) with a structure in which microcapsules enclosing a dispersion of electrophoretic particles are arranged between opposed electrode substrates. As compared with the conventional electrophoretic display devices, the microcapsule type electrophoretic display devices are remarkably improved in various performances and functions, such as long-term stability of display, responsiveness, contrast, and display rewritable times.
For the electrophoretic display devices, there have also been proposed, besides fixed equipments such as ordinary displays, techniques of flexible displays, which have the shape of a thin sheet, which are ultraportable, and which can freely be inflected, such as electronic papers and electronic books.
In such electrophoretic display devices, there has been proposed a technique of making a dispersion of electrophoretic particles, i.e., a dispersion for electrophoretic display devices, into microcapsules (e.g., see Japanese Patent Laid-open Publication No. 2002-526812). A flexible sheet-shaped electrophoretic display device can easily be produced by enclosing a dispersion for electrophoretic display devices in microsphere-shaped microcapsules made of a transparent resin or the like and allowing the thus obtained microcapsules for electrophoretic display devices to be supported on the surface of an electrode film. There occurs neither uneven local distribution nor movement of a dispersion for electrophoretic display devices by making the dispersion for electrophoretic display devices into microcapsules, resulting in a technique also suitable for various applications in which electronic equipments may variously change their positions or may be inflected when used, such as electronic papers.
A flexible sheet-shaped electrophoretic display device is produced, for example, by applying a coating solution containing microcapsules for electrophoretic display devices and a binder resin to an electrode film, thereby forming a data display layer on an electrically conductive layer of one electrode film, and subsequently attaching the other electrode film onto the data display layer. At that time, the microcapsules are arranged on the electrode film without any gaps in the in-plane direction and without any stacking in the thickness direction, to thereby obtain higher contrast.
As a method of arranging microcapsules on an electrode film without any gaps in the in-plane direction and without any stacking in the thickness direction, there have been studied, for example, a method of applying a coating solution containing microcapsules and a binder resin on an electrode film, and subsequently allowing the microcapsules on the electrode film to move in a specified direction for gathering (e.g., see Japanese Patent Laid-open Publication No. 2005-70567), and a method of applying a coating solution containing microcapsules and a binder resin on an electrode film, and subsequently applying the coating solution again to fill the gaps between the microcapsules on the electrode film (e.g., see Japanese Patent Laid-open Publication No. 2005-84267).
In the heretofore known methods as described above, however, even if the microcapsules on the electrode film are allowed to move in a specified direction for gathering or a coating solution is applied again to fill the gaps between the microcapsules on the electrode film, the stacking of the microcapsules in the thickness direction cannot necessarily be suppressed to a satisfactory extent, and therefore, there have been some cases where high contrast cannot be obtained. In addition, even if high initial contrast can be obtained, the variation of contrast with time is great, and therefore, there have been some cases where practical utility is deteriorated.